The NCS will employ a national probability sampling approach to select locations and participants for conduct of the study. The sampling design utilizes a multistage clustered approach. In the first stage, 105 locations (generally corresponding to single counties) were randomly selected from all U.S. counties. Seven of the locations serve as the initial or Vanguard Locations, participating in the pilot phase of the NCS. Because the focus of the study includes assessment of the impact of exposures that occur early in pregnancy, both pregnant women and their partners, and women of childbearing age, comprise the initial target population for enrollment. Data will be collected in combinations of face-to-face contacts and remote collection methods, e.g., telephone, computer, or mail-in questionnaires. The expected frequency of contact (face-to-face or remote) is approximately every three months through age one, every six months through age five years and annually thereafter. For a sample of children enrolled in the study, visits will also be made to child care and school settings for collection of environmental samples and observational data. Anticipated biologic specimens include blood, urine, hair, and nail clippings from mothers and children;blood, urine, and hair from fathers;cord blood, umbilical cord and placental tissues, and meconium collected at/around the time of delivery;vaginal swabs, and breast milk from mothers. Anticipated environmental samples include air, dust, soil, food, and water. .